With widespread use of mobile telecommunications such as portable phones, there is an upward trend in use of mobile communication devices that have facilities to use two different communication systems such as the dual-band cellular telephone system.
Any such telecommunication device hitherto often shares an antenna for both of the two communication systems. The device requires two channels of transmitter circuit and receiver circuit independently for the respective communication systems. Each of them is selected with a switch for making a communication. In general, a high frequency section in any of these transmitter circuits comprises a power amplifier, a low pass filter, and the like. A high frequency section in any of the receiver circuits comprises an impedance matching circuit, a surface acoustic wave filter (hereinafter referred to as SAW filter), and the like.
One of these transmitter circuits and receiver circuits is put into connection with the antenna when in operation. For this purpose, a transmitter/receiver switching circuit using a PIN diode is provided at an antenna side of each circuit, and it is operated under the control of a logic circuit. Telecommunication is thus accomplished in any of the two different communication systems.
Normally, high frequency sections of the mobile communication devices are modularized and built into the devices for simplification of the design and manufacturing ease of the communication devices in most cases. They are frequently called high frequency composite switch modules, high frequency circuit modules, high frequency front-end modules and the like.
FIG. 12 and FIG. 13 show one example of the high frequency composite switch modules which have been used heretofore in the mobile communication devices designed for two different communication systems. FIG. 12 is an exploded perspective view, and FIG. 13 is a block diagram of the same.
In this module, a wiring pattern of a transmitter/receiver switching circuit, i.e. the switching circuit for selecting between a transmission signal and a reception signal, and low pass filters (LPF) 1206 in transmitter circuits shown in FIG. 13 are composed of conductor patterns 1202 disposed inside a multilayer board formed by stacking a plurality of dielectric layers 1201, as shown in FIG. 12. Besides, PIN diodes 1203, SAW filter 1204, and chip components 1205, which constitute the switching circuit, are mounted on an outer surface of the multilayer board.
In this device here, the SAW filter 1204 is used as a band pass filter (BPF) of the receiver circuit shown in FIG. 13.
Also, Single-Pole Double-Throw (SPDT) switch 1207 is composed of conductor patterns 1202 in the multilayer board, PIN diodes 1203 and chip components 1205.
A power amplifier is not included in this module, but it is arranged separately for the reason of heat and dimension. As a result, it requires additional transmission lines as signal paths for connection between the module and the power amplifier. Moreover, it is necessary to separately provide additional wiring for power supply to both of these components.
Furthermore, this module uses a switching circuit having PIN diodes for selection between the two communication systems as well as between the transmission and reception signals. This module contains four PIN diodes, chip components and wiring patterns as the constituent components. Consequently, a scale of the circuit becomes inevitably large, the circuit structure becomes complicated, and a large number of components also become necessary. Accordingly, since they increase a transmission loss in the signal wires, a transmission power at an antenna end and a receiving power at an input terminal of the receiver circuit decrease to that extent. In other words, an overall efficiency of the mobile communication device decreases in respect to the transmission power and the receiving power.